In the eastern suburbs if you can get atleast a 90 you are doing good, in like Berwick you are doing great if you get atleast 80.
I don't really agree with this statement. I don't think a school's culture can create the difference between 80 and 90. It can create some difference, but I don't think that many of the high 99 kids at elite private/selective schools would be getting 80s if they went to a local school in Berwick or Werribee. They may get less for one reason or another but they would still do well. Also remember that many of the people that succeed at selective schools have a local public primary school and local state secondary school background.
I think it can, especially when you have an isolated community (whether that be in outer suburbia or the country). VCE scores are largely about motivation and resources, and if you have students who really don't care either way, they're not going to do amazingly, irrespective of their intelligence. Certain environments will affect individuals differently, and you're always going to have the handful that
I think my cousin epitomises this. She did well - about 95 - but in primary school she was winning major prizes in national competitions, as well as high distinctions in the majority of competitions she entered. She's now at Melbourne Uni, attaining straight HDs whilst still maintaining a social life. If she'd been at an elite private school in VCE, she would've had a shot at high 99s, if not a 99.95 if she'd knuckled down. She worked in high school, but she wasn't really pushed to succeed and she could've done much better. That said, she didn't get dux of her high school - she just missed out, but her score's incredible considering the number of other things she did in the year (many of which were very social). She went to a country school which didn't have a very academic ethos (most of the kids who did end up going to University didn't even apply for G8 institutions and most didn't apply full stop).
To summarise my ramblings, everyone's affected differently by scenarios, but often the culture of a school will affect certain exceptionally intelligent individuals in a very negative manner.